1. Technical Field of the Invention
The present invention relates to oil-in-water photoprotective emulsions in which the oil globules of the emulsion have an average diameter of at most 500 nm, containing at least particles of ionic polymer and at least one UV radiation-screening system, which screening system comprises at least one UV-A-screening agent of the 4,4-diarylbutadiene type.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation having wavelengths of between 280 nm and 400 nm allows tanning of the human epidermis, and that rays having wavelengths of between 280 nm and 320 nm, known by the name UV-B, cause erythemas and skin burns which can hamper the development of the natural tan; this UV-B radiation must therefore be screened out.
It is also known that UV-A rays having wavelengths of between 320 nm and 400 nm, which cause tanning of the skin, are capable of inducing its impairment, in particular in the case of a sensitive skin or a skin continually exposed to solar radiation. UV-A rays cause in particular a loss of elasticity of the skin and the appearance of wrinkles which lead to premature aging. They promote the onset of the erythematous reaction or amplify this reaction in some subjects and may even be responsible for phototoxic or photoallergic reactions. It is therefore desirable to also screen out UV-A radiation.
UV-A and UV-B rays must therefore be screened out and protective cosmetic compositions for the human epidermis containing UV-A- and UV-B-screening agents currently exist.
For various reasons linked in particular to their great comfort in use and to their refreshing property, cosmetic compositions, and in particular those intended for photoprotecting the skin against UV-A and UV-B rays, called antisun/sunscreen compositions, are most often provided in the form of an emulsion of the oil-in-water type, containing an oily phase homogeneously dispersed in an aqueous phase. In these conventional emulsions, which contain emulsifying agents (or surfactants) and optional cosmetic additives, the size of the globules constituting the fatty phase is generally greater than several microns. Such emulsions may have inadequate cosmetic properties (oily feel) and physical properties (stability).
One of the major objectives of the antisun/sunscreen compositions of the O/W type known to date is to have perfect emulsion stability combined with photoprotection which is as broad as possible and improved safety. The expression stability of the emulsion is understood to mean that the dispersion remains macroscopically and microscopically (particle size) stable over a period of time of at least 30 days.
Moreover, it is observed that despite the presence of emulsifying agents (or surfactants), some of these emulsions exhibit a lack of stability over time, a lack of stability resulting in the appearance of a phenomenon of separation (phase separation) between the aqueous and oily phases of the emulsion. This instability hampers the preservation of the emulsions.
Accordingly, to avoid this undesirable phenomenon, it is often necessary to resort to so-called thickening agents, which are then introduced into the emulsion and whose primary function is to create, in the aqueous phase, a gelled matrix which serves to immobilize the globules of the fatty phase within its three-dimensional network, thus ensuring mechanical preservation of the whole emulsion. However, this addition of thickening agent limits the galenic forms which are possible, by excluding in particular very fluid compositions.
To date, it is increasingly sought to prepare fluid, in particular antisun, compositions, more especially with the aim of having easily vaporizable products which are often considered by the user as being easier to apply than creams.
Finally, to limit as much as possible the risks of intolerance, in particular of so-called “sensitive” skins, it is increasingly sought to limit as much as possible, in the manufacture of oil/water emulsions, the use of emulsifying surfactants which, through their action, can make fragile the barrier function of the epidermis.
To remedy these problems and to respond to these needs, particularly stable fine and fluid emulsions containing and stabilized by particles of ionic polymer have been developed in EP-0-864,320, the oil globules of these emulsions having an average diameter of less than 500 nanometres. These emulsions have particularly satisfactory sensory qualities (feel). These emulsions may be used for photoprotecting the skin and the hair against the effects of UV rays since they can contain UV-A screening agents and/or UV-B-screening agents.
Among the available organic UV-A-screening agents, a family of compounds which are particularly effective in the UV-A region is 1,4-benzene[di(3-methylidene-10-camphorsulfonic)] acid and its different salts, which is described in particular in FR-A-2,528,420 and FR-A-2,639,347; they are indeed capable of absorbing ultraviolet rays having wavelengths of between 280 nm and 400 nm, with absorption maxima of between 320 nm and 400 nm, in particular in the region of 345 nm.
However, the introduction of this type of UV-A-screening agent, even sometimes in low doses, into fine oil-in-water emulsions stabilized with particles of ionic polymer rapidly leads to their destabilization. This forces the formulator to use them in very low concentrations and to limit the photoprotective efficacy in particular in the UV-A domain.
It thus appears necessary to provide fine antisun/sunscreen oil-in-water emulsions based on particles of ionic polymer which are stable and which may contain organic screening agents active in UV-A of comparable efficacy to that of 1,4-benzene[di(3-methylidene-10-camphorsulfonic)] acid and its different salts without the disadvantages listed above.